The present invention relates to an improvement in the counting characteristics of a particle detector and a neutron detector that use ZnS phosphors.
Conventional detectors of particles such as alpha particles or conventional neutron detectors which detect neutrons indirectly by detecting the particles emitted from the neutron converter 6Li or 10B have in most cases used ZnS phosphors since they have considerably high fluorescence yields in response to incident particles and the short-lived components of fluorescence have decay times of only 200-300 ns.
However, the fluorescence from ZnS phosphors contains the long-lived components that contribute “afterglow” effects as shown in FIG. 12. Hence, the mean life of fluorescence from ZnS phosphors is said to range from 70 to 100 μs. On account of those long-lived components, the incidence of high-rate particles or neutrons can cause a “pile-up” of pulses, making it difficult to measure accurate counting rates (see Hoshasen Handbook, 2nd Ed.)
As the operation of the high-intensity pulsed neutron source using a high-intensity proton accelerator has made a progress in recent years, the ranges of the intensity of pulsed neutrons and the neutron energy produced have both expanded and it is now essential to develop a detector that is capable of convenient neutron detection and two-dimensional neutron imaging without being saturated even if neutrons are incident at high rates. Measurement of particles at high counting rates is also essential in experiments using an accelerator or a nuclear reactor. In the measurement of neutrons or particles, they must be detected with reduced effects of gamma rays as the background. Detection of particles with the least possible quantities of gamma rays as the background is also indispensable to observations of dark matter or cosmic rays.